1. Field of the Invention
Curable compositions, such as benzoxazine-based ones, are useful in applications within the aerospace industry, such as for example as a heat curable composition for use as a matrix resin or an adhesive, and form the basis of the present invention, in which the curable composition is filled with silica having a mean particle diameter on the order of 10−9 meters.
2. Brief Description of Related Technology
Epoxy resins with various hardeners have been used extensively in the aerospace and electronics industries both as adhesives and as matrix resins for use in prepreg assembly with a variety of substrates.
Benzoxazines themselves have been reported in the literature as generally having a high glass transition temperature, good electrical properties (e.g., dielectric constant), and low flammability.
Blends of epoxy resins and benzoxazines are known. See e.g. U.S. Pat. Nos. 4,607,091 (Schreiber), 5,021,484 (Schreiber), 5,200,452 (Schreiber), and 5,445,911 (Schreiber). These blends appear to be potentially useful in the electronics industry, as the epoxy resins can reduce the melt viscosity of benzoxazines allowing for the use of higher filler loading while maintaining a processable viscosity. However, epoxy resins oftentimes undesirably increase the temperature at which benzoxazines polymerize.
Ternary blends of epoxy resins, benzoxazine and phenolic resins are also known. See U.S. Pat. No. 6,207,786 (Ishida), and S. Rimdusit and H. Ishida, “Development of new class of electronic packaging materials based on ternary system of benzoxazine, epoxy, and phenolic resin,” Polymer, 41, 7941-49 (2000).
U.S. Pat. No. 6,323,270 (Ishida) speaks to and claims a nanocomposite composition of clay and a benzoxazine monomer, oligomer, and/or polymer in amount effective to form a nanocomposite. The clay is described as a silicate comprised of multiple platelets, or a hydrated aluminum silicate comprised of multiple platelets. Clay, reads the '270 patent, is a component of soils typically derived from the weathering of rocks that can be an aggregate having particle sizes of less than about 200 microns, such as less than about 100 microns, like less than about 50 microns, examples of which being montmorillonite, atapulgite, illite, bentonite, and halloysite.
Notwithstanding the state of the technology, there has been no disclosure, teaching or suggestion to prepare a heat curable composition based on the combination of a benzoxazine and silica having a mean particle diameter on the order of 10−9 meters, let alone one with improved performance properties.